Abstract
The one-electron reduction kinetics of the europium cryptates Eu(2.2.1)3+ and Eu(2.2.2)3+ by the aquo ions Vaq 2+ and Euaq 2+ and the oxidation kinetics of Eu(2.2.1)2+ by Co(NH3)6 3+ have been studied by using a polarographic technique in order to examine the effects of encapsulating europium within cryptate cavities upon the reactivity of the Eu(III/II) couple. At 25°C and an ionic strength μ = 0.1, the second-order rate constants (M-1 s-1) for acid-independent pathways are as follows: Eu(2.2.1)3+-Vaq 2+, 0.5; Eu(2.2.1)3+-Euaq 2+, ca. 0.2; Eu(2.2.2)3+-Euaq 2+, 1.5; Eu(2.2.2)3+-Euaq 2+, 1.4; Co(NH3)6 3+-Eu(2.2.1)2+, 0.055. By comparison of these kinetic data with those for similar reactions involving the Euaq 3+/2+ couple, the rate constant for Eu(III/II) self-exchange, kex, is estimated to increase by factors of ca. 1 × 107 and 2 × 104 upon encapsulation of europium in (2.2.1) and (2.2.2) cryptate cavities, respectively. Estimates of kex equal to ca. 10, 4 × 10-2, and 5 × 10-6 M-1 s-1 (μ = 0.1) for Eu(2.2.1)3+/2+, Eu(2.2.2)3+/2+, and Euaq 3+/2+, respectively, are obtained from the Marcus cross relation. The increases in kex resulting from cryptate encapsulation suggest that nonadiabaticity is not primarily responsible for the extremely low reactivity of Euaq 3+/2+. The values of kex are shown to be roughly consistent with the Franck-Condon barriers estimated from structural data.
| Original language | English |
|---|---|
| Pages (from-to) | 3465-3470 |
| Number of pages | 6 |
| Journal | Inorganic Chemistry |
| Volume | 22 |
| Issue number | 23 |
| Publication status | Published - 1983 |
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- Inorganic Chemistry
Cite this
The nonadiabaticity question for europium(III/II) : Outer-sphere reactivities of europium(III/II) cryptates. / Yee, Edmund L.; Hupp, Joseph T; Weaver, Michael J.
In: Inorganic Chemistry, Vol. 22, No. 23, 1983, p. 3465-3470.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The nonadiabaticity question for europium(III/II)
T2 - Outer-sphere reactivities of europium(III/II) cryptates
AU - Yee, Edmund L.
AU - Hupp, Joseph T
AU - Weaver, Michael J.
PY - 1983
Y1 - 1983
N2 - The one-electron reduction kinetics of the europium cryptates Eu(2.2.1)3+ and Eu(2.2.2)3+ by the aquo ions Vaq 2+ and Euaq 2+ and the oxidation kinetics of Eu(2.2.1)2+ by Co(NH3)6 3+ have been studied by using a polarographic technique in order to examine the effects of encapsulating europium within cryptate cavities upon the reactivity of the Eu(III/II) couple. At 25°C and an ionic strength μ = 0.1, the second-order rate constants (M-1 s-1) for acid-independent pathways are as follows: Eu(2.2.1)3+-Vaq 2+, 0.5; Eu(2.2.1)3+-Euaq 2+, ca. 0.2; Eu(2.2.2)3+-Euaq 2+, 1.5; Eu(2.2.2)3+-Euaq 2+, 1.4; Co(NH3)6 3+-Eu(2.2.1)2+, 0.055. By comparison of these kinetic data with those for similar reactions involving the Euaq 3+/2+ couple, the rate constant for Eu(III/II) self-exchange, kex, is estimated to increase by factors of ca. 1 × 107 and 2 × 104 upon encapsulation of europium in (2.2.1) and (2.2.2) cryptate cavities, respectively. Estimates of kex equal to ca. 10, 4 × 10-2, and 5 × 10-6 M-1 s-1 (μ = 0.1) for Eu(2.2.1)3+/2+, Eu(2.2.2)3+/2+, and Euaq 3+/2+, respectively, are obtained from the Marcus cross relation. The increases in kex resulting from cryptate encapsulation suggest that nonadiabaticity is not primarily responsible for the extremely low reactivity of Euaq 3+/2+. The values of kex are shown to be roughly consistent with the Franck-Condon barriers estimated from structural data.
AB - The one-electron reduction kinetics of the europium cryptates Eu(2.2.1)3+ and Eu(2.2.2)3+ by the aquo ions Vaq 2+ and Euaq 2+ and the oxidation kinetics of Eu(2.2.1)2+ by Co(NH3)6 3+ have been studied by using a polarographic technique in order to examine the effects of encapsulating europium within cryptate cavities upon the reactivity of the Eu(III/II) couple. At 25°C and an ionic strength μ = 0.1, the second-order rate constants (M-1 s-1) for acid-independent pathways are as follows: Eu(2.2.1)3+-Vaq 2+, 0.5; Eu(2.2.1)3+-Euaq 2+, ca. 0.2; Eu(2.2.2)3+-Euaq 2+, 1.5; Eu(2.2.2)3+-Euaq 2+, 1.4; Co(NH3)6 3+-Eu(2.2.1)2+, 0.055. By comparison of these kinetic data with those for similar reactions involving the Euaq 3+/2+ couple, the rate constant for Eu(III/II) self-exchange, kex, is estimated to increase by factors of ca. 1 × 107 and 2 × 104 upon encapsulation of europium in (2.2.1) and (2.2.2) cryptate cavities, respectively. Estimates of kex equal to ca. 10, 4 × 10-2, and 5 × 10-6 M-1 s-1 (μ = 0.1) for Eu(2.2.1)3+/2+, Eu(2.2.2)3+/2+, and Euaq 3+/2+, respectively, are obtained from the Marcus cross relation. The increases in kex resulting from cryptate encapsulation suggest that nonadiabaticity is not primarily responsible for the extremely low reactivity of Euaq 3+/2+. The values of kex are shown to be roughly consistent with the Franck-Condon barriers estimated from structural data.
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M3 - Article
VL - 22
SP - 3465
EP - 3470
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 23
ER -